1. Field of the Invention
The invention relates to a means of regenerating ammoniacal etching solutions used for etching metallic copper and somewhat more particularly to a method of regenerating spent ammoniacal etching solutions used in etching galvanized printed circuits and the like.
2. Prior Art
Ammoniacal etching solutions used for etching galvanized printed circuits are known. For example, German Offenlegungsschrift (DT-OS) 26 25 869 suggests the use of aqueous ammoniacal solutions in etching copper-laminated printed circuits. These etching solutions contain tetrammine copper (II) ions, ammonia and ammonium salts. During the etching of metallic copper with such a solution, the following reaction occurs: EQU Cu+[Cu (NH.sub.3).sub.4 ].sup.++ .fwdarw.2 [Cu (NH.sub.3).sub.2 ].sup.+(A)
tetrammine cupric ions, PA1 diammine cuprous ion,
Active PA2 Inactive EQU 2 [Cu(NH.sub.3).sub.2 ].sup.+ +2NH.sub.3 +2NH.sub.4.sup.+ +1/2O.sub.2 .fwdarw.2[Cu(NH.sub.3).sub.4 ].sup.++ +H.sub.2 O (B)
The sum of reaction equations (A) and (B) provides an overall reaction, (C) as follows: EQU Cu+2NH.sub.3 +2NH.sub.4.sup.+ +1/2O.sub.2 .fwdarw.[Cu(NH.sub.3).sub.4 ].sup.++ +H.sub.2 O (C)
In the above reactions, O.sub.2 can be derived from atmospheric oxygen. Atmospheric oxidation of Cu.sup.+ to Cu.sup.++ takes place substantially spontaneously in a spray etching machine so that a separate air supply is not required.
The above referred DT-OS suggests that the ammonium salts are, preferably, comprised of a mixture of NH.sub.4 Cl and (NH.sub.4).sub.2 CO.sub.3. In its salt form, the overall reaction, for example with the chloride salt, appears as follows: EQU Cu+2NH.sub.3 +2NH.sub.4 Cl+1/2O.sub.2 .fwdarw.[Cu(NH.sub.3).sub.4 ]Cl.sub.2 +H.sub.2 O (D)
From the foregoing, it can be seen that metallic copper, with the consumption of ammonia, ammonium salts and atmospheric oxygen, is oxidized to [Cu(NH.sub.3).sub.4 ].sup.++ ions. During operation of the etching process the chemicals, NH.sub.3 and NH.sub.4 salts are added as needed to the etching machine via an aqueous solution, sometimes referred to as a "supplementary solution" or replenisher.
The spent etching solution contains a relatively high copper concentration and is collected as waste. This waste etching concentrate is sent to a separate copper processing operation where, apparently, the NH.sub.3 is reacted with chlorine and the copper is precipitated out with scrap iron (Fe). The handling of the waste in this operation is combined with transport and processing costs.